The present invention relates to hydraulic valve lifters for internal combustion engines; more particularly, to hydraulic valve lifters filled with oil during manufacture; and most particularly, to hydraulic valve lifters which are refillable after assembly to ensure a desired volume of fill oil.
Hydraulic valve lifters are well known in the internal combustion engine art, especially for pushrod-type engines wherein a cam-actuated lifter, acting on a pushrod, actuates a valve stem via an intermediate rocker arm. A lifter for each intake and exhaust valve is slidingly disposed in the engine block between the pushrod and its corresponding cam lobe and translates the cam rotary motion into pushrod linear motion to open and close the valve. Typically, a hydraulic lifter has an outer body actuated by the cam lobe, which body may contain a roller for riding on the cam. The outer body is hollow and defines a well, opening away from the cam lobe and containing a close-fitting plunger which is axially slidable within the well. The upper end of the plunger is closed by a hollow seat for supporting a spherical end of the pushrod. Engine oil under pressure is provided, via a port in the outer body to a low-pressure chamber within the plunger. A check valve connects the low-pressure chamber to a high-pressure chamber formed between the bottom of the well and the plunger, which chamber is expanded by a plunger spring to urge the plunger axially with respect to the well until all mechanical lash in the train between the cam lobe and the valve stem is eliminated, thus rendering the train compressionally rigid. Typically, with each compressive stroke of the lifter, a small amount of oil is expressed from the high pressure chamber, which amount is replaced during the recovery portion of the stroke from the low-pressure chamber via the check valve.
The low-pressure chamber also opens onto the pushrod seat for providing engine oil to the engine rocker arm assembly, via axial passages in the seat, the ball end, and the pushrod. To maintain high oil pressure in the rest of the oil supply system, a simple metering valve is provided in the lifter. The oil-entry side of the pushrod seat is formed having a transverse cylindrical surface, the pushrod seat oil passage opening into the curved surface. A disk-shaped metering plate is supported within the plunger by an annular feature formed at the upper end of the low-pressure chamber between the low-pressure chamber and the pushrod seat. The plate is permitted an axial range of motion between the seat and the annular feature. Oil flowing upwards from the low-pressure chamber to the pushrod urges the plate against the entry to the pushrod seat oil passage which thus becomes partially but not fully sealed by the plate because the cylindrical surface curves away from the plate. Thus, a predetermined leakage area is established between the metering plate and the pushrod seat. Sufficient oil is passed to lubricate the engine top elements, while the engine oil pressure is maintained. When the engine is shut off, oil flow stops and the plate settles by gravity onto the annular feature, forming a check valve against gravity drainage of oil from the pushrod.
There are at least two circumstances wherein the check valve action of the metering plate can be undesirable.
First, pushrod lifters may be used in V-style engines, wherein the lifters are canted at an angle from vertical. This orientation can allow oil in the low-pressure chamber to drain back into the engine via the oil supply port when the engine is shut off. Significant noise from mechanical lash can result at the ensuing engine startup, until the lifter is refilled from the engine oil supply. The volume of oil retained within the pushrod is relatively large, but because of the check-valve action of the metering plate on the annular feature, this pushrod reservoir is trapped in the pushrod and is not available to drain into the low-pressure chamber by gravity flow during periods of engine inactivity.
Second, prior to shipment of lifters from a manufacturing facility to an engine assembly site, typically the high-pressure chamber is filled with a low-viscosity fluid such as kerosene and the low-pressure chamber is filled with a low-viscosity oil such as 5W30 grade. During assembly of the lifter, especially a valve-deactivating lifter, it is a known problem to lose some of these fluids such that, when ready for shipment, the low-pressure chamber is only partially filled, which partial filling is not readily detected until installation in an engine. Such a deficient lifter, when installed in an engine being assembled, will clatter upon actuation by the engine, resulting in immediate rejection of the engine on the assembly line. Such failure is very costly in terms of engine rework, and can result in an engine manufacturer""s switching to a different supplier of lifters. In prior art hydraulic lifters, the check-valve action of the metering plate on the annular feature prevents injection of oil into the low-pressure chamber through the pushrod seat as a corrective measure after assembly of the lifter, as might be undertaken to ensure that the low-pressure chamber is correctly filled immediately prior to shipment.
It is a principal object of the present invention to provide an improved hydraulic valve lifter wherein a metering plate cooperating with retaining means in a low-pressure chamber is incapable of forming a reverse-flow check valve.
Briefly described, an improved oil metering valve means in a hydraulic valve lifter is configured such that a metering plate cooperates with a pushrod seat to meter the flow of oil in a first direction, as in the prior art. The metering means is also conducive to the flow of oil in a second and reverse direction and does not define a reverse-flow check valve. Embodiments of such oil metering valve means may include, but are not limited to: a metering plate having one or more notches around its periphery to permit oil to flow past the plate and an annular feature supporting the plate; a metering plate having one or more apertures to permit oil to flow through the plate; a metering plate having one or more nonplanar areas along its edges to prevent sealing of the plate against the annular feature; and one or more irregularities in the annular feature, such as grooves, bumps, or undulations to permit flow around the edge of the plate.